text:
What permissions or approval are needed to land in Antarctica?
Can I land at Jack F. Paulus Skiway (NZSP) with just an ATC clearance? Or do I need to ask some other authority before I fly there? Are there any regulations regarding 'landing rights' in Antarctica?
Edit:
Let's assume I am in a private aircraft that is able to safely fly to NZSP where I am flying under IFR. Do I still need permission from some kind of authority? And what about commercial flying?

That would no doubt depend on the country operating the base. AFAIK you'd need for example a Chilean visa before visiting their bases.

For this we need to reference the US Antarctic Program Inter-agency Air Operations Manual
First off this will tell us who is in charge down there (at least for US bases) as its not quite an ice frontier free for all,

Oversight of the on-ice operations of the civil aircraft is
  NSF-delegated to the Dept of the Interior/OAS Office of Aviation
  Services (OAS) in accordance with the SLA between OAS/AIL. Joint use
  of the USAP airspace in Antarctica requires close coordination between
  the DoD and NSF (and its delegations).

It looks like if you want to fly down there you need to file form DD 1801

2.3.4. Intercontinental flights between New Zealand and Antarctica will require USAP aircrew to file a DD Form 1801 (International Flight
  Plan) in Christchurch Base Operations to Christchurch Clearance
  Delivery. Flights utilizing the Macquarrie route will require a FIR
  estimate for Melbourne and Auckland boundaries.

The document does not list any approach procedures for NZSP but it does list them for McMurdo Station and they are presumably similar,

2.7.2.1. IFR. McMurdo ATC retains responsibility for all IFR aircraft. Aircraft will be  USAP Inter-agency Air Operations Manual, 1 August
  2012 40 instructed to contact Tower prior to entering Class E
  airspace. Mac
2.7.2.2. VFR. Aircraft are normally instructed to contact tower no closer than 10 miles from the airport for landing instructions.
2.7.2.3. Aircraft operating in Class D airspace will be in radio contact with the tower and should remain at 1,000 feet AGL or higher
  (500 feet for helicopters) until commencing final descent.

They even have reg's for uncontrolled fields

2.8.1. For operations at uncontrolled McMurdo area airfields, fixed/rotary wing aircraft pilots will follow uncontrolled field
  procedures.
2.8.1.1. Flight plans will be filed with Mac Center and advisory service provided.
  2.8.1.2. Fifteen (15) minutes prior to departure from an uncontrolled airfield, the pilot will notify Mac Center/Tower of planned activity
  via landline or radio.
2.8.1.3. Mac Center/Tower will notify Aircraft Rescue and Fire Fighting (ARFF) (who notifies the USAP Airfield Manager) on FM Channel
  2 of intended uncontrolled airfield operations.
2.8.1.4. Pilots will announce their intentions on the Common Traffic Advisory Frequency (CTAF) VHF 129.7 MHz.

Interestingly it looks like McMurdo is the primary landing strip however based on the letter of 1.2.1 the South Pole Station (which Im pretty sure is NZSP) only accepts ski equipped aircraft so you would at least need skis.

1.2.1. Primary airfields for the USAP are located in the McMurdo Station area and at the South Pole Station (ski-equipped aircraft
  only). The primary heliport is located at McMurdo Station. Additional
  ice runways, skiways, and helicopter landing sites are established
  throughout the continent supporting the USAP science activities as
  planned by the NSF Prime Contractor’s Fixed/ Rotary Wing Coordinators.

According to the doc a lot of the info is published in the Antarctic Flight Information Manual which looks like you may need to set up some kind of account here to download or "contact [your] affiliate National Antarctic Program".
All this in mind, I have not yet found any documentation or out right publications that seem to forbid flying there as long as procedures are followed. With that in mind you clearly need to file some flight plans and related info, I would think you would need a good reason to be going there to get approval. The reality is there may be more info on this buried in the antarctic treaty but in practice I dont know how that sort of stuff gets enforced.


text:
Can I use a personally owned aircraft in the EU for PPL flight training?

Can I use my own C152 to gain my PPL (EASA) with a qualified instructor?
Is this a considered a commercial flight?
Can you define a 'training flight'?
Is hour building a commercial flight?
If I use my private 152 how about insurance?

Yes. No. Flight with instructor towards gaining a new rating or license. Can be, depends. What about the insurance? :)

Actually training flight can be with or without instructor (solo), but a flight you're not qualified to undertake without an instructor or an endorsement

Welcome to Aviation.SE! Since you have 5 different (though related) questions, a better fit for the StackExchange model would be to ask 5 different questions. Please feel free to do so, nobody will get mad at you for it. You can reference one from another, just to help tie them together, if you'd like.

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sort: votes


text:
Do aircraft engineers take into consideration engine placement to avoid ground strikes in a cross-wind landing?
On a multi-engine airplane with wing-mounted engines, do aircraft designers have a standard way of ensuring that the banked landings associated with cross-wind's do not cause a prop or engine-housing strike on the ground if the pilot were to over-bank?
Is there some rule such as, "the wing tip would need to be the first part to strike if the wheel is in contact with the ground", or similar standard of practice in design?

There are videos out there of jets dragging engines on the runway.

This is not opinion based.  There either is a rule or there is not a rule.  You not knowing does not make it someone else's opinion.

For jet aircraft, there is no rule about preventing a nacelle from contacting the ground before the wingtip. There will be a design requirement that the airplane can touch down at a certain angle of bank and have the landing gear touch down but not strike a nacelle or wing, but not whether nacelle or wing must strike first. The nacelle is already designed for a wheels-up landing, so it's possible it could survive better than a wing tip. While it's certainly more of a risk on 4-engine aircraft, it can also happen on twin jets.
Propeller aircraft are typically designed such that gear and wingtip will make contact without the propeller making contact, either through having gear directly below props on a low-wing configuration, or through a high-wing configuration. While a jet engine nacelle can sustain some structural damage in a strike, it will typically not affect the engine's operation. If a propeller gets damaged it could cause that engine to become unusable, making it much more difficult for the crew to successfully perform a go-around.

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text:
What is "one flat movement" of a screw on the fuel control unit?
I'm looking to do a N1 low idle speed adjustment oa King Air B350 with the PT6A-60A engine. There is a note saying that one flat movement of the low idle speed screw in the FCU increases N1 by 3.5%
What is "one flat movement" in this context?

Welcome to the site! Which aircraft are you asking about, and do you have a picture or exact quote of the note?

I'm not a mechanic, but I'm guessing that it means that you are turning the adjustment screw with a flat headed screwdriver, in which case it would be 180 degrees (turning the "flat" part over).

The aircraft is king air b350 engine pt6a-60a there are 2 screw in one line request to loosen one screw and tighten the other to increase or decrease the n1

The note mentioned that the one flat movement of the screw increasing the n1 by 3.5%

Consider a nut or a bolt with a hexagonal shape. It has six flats in three parallel pairs. Turning one of these nuts or bolts by one flat would thus refer to turning it by one-sixth of a complete rotation, ie by 60 degrees. Other nuts and bolts, also some screws, may have other numbers of flats. A Wikipedia page has dimensions across the flats.

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text:
Is a weather briefing required?
Are pilots legally required to obtain a weather briefing prior to some or all flights?

Which jurisdiction?

Jurisdiction does not matter. It would be interesting to know if any jurisdiction has addressed this issue in any way.

Actually, you are asking about legality, so jurisdiction does matter.  We can not possibly answer for every country in the world, and we require each question to be able to be answered with one answer.  Please do specify the jurisdiction so that your question does not get closed as "too broad".  For more info, see [ask].

No weather briefing is required.

According to the NTSB, the simple answer is NO (you aren't legally required to call the FSS). The NTSB states...
  Part 91 regulations do not specifically require the use of any particular sources of weather information for GA pilots, but do require that all pilots familiarize themselves with weather and weather forecast information before beginning a flight. Source.

"The NTSB states [...] Part 91 regulations [...] do require that all pilots familiarize themselves with weather and weather forecast information before beginning a flight." Doesn't this suggest that some form of weather briefing is required (at least in the US)?

It depends on the definition of "briefing", which is still largely interpreted to mean communication with another human being. Therefore, looking at TV, Internet forecasts or news papers is not considered a "briefing" but is considered "familiarization". This is the vernacular meaning as used by the NTSB.

Yes, at least for flights that are not in the "vicinity" of the airport.
FAA CFR 91.103

Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include--
(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

You are not required to call Flight Services for a weather brief, but you are required to get the weather reports (which can be called a personal brief). If you do all flight services and happen to have an accident, then your accident will contain the details about your call.

As I understand its wording, this answer does not appear to be correct. While §91.103 does require the pilot to "become familiar with", this does not translate to a requirement for a weather briefing. The pilot may become familiar with the pertinent information through means such as looking directly at weather reports. A weather briefing is a human or machine prepared gathering of information specific to a flight or location.

@JWalters You can self-brief. A weather "briefing", to me, just means looking at prepared weather data, be it a METAR or TAF. I'm not sure how it would not fall under "human or machine prepared" and "information specific to a flight", you wouldn't look at LAX weather if you were flying in ATL...

Most airlines nowadays only have briefings at their base/hubs. On the line stations they would probably get handed a 'briefing package' consisting of an Operational flight plan, Weather, Notams (and company notams), charts (pressure and volcanic ash etc), this would be printed out by the station staff or handling agent. The station staff will add more info like the special load notification, Dangerous goods notification. In some cases like for short hops the station may print out the actual weather (METAR) at the destination and alternates.


text:
Why is an auditory alarm necessary when the autopilot disengages?
The FAA gives one requirement for the autopilot in the following FAR...

FAR §25.1329 Flight guidance system.
(j) Following disengagement of the autopilot, a warning (visual
  and auditory) must be provided to each pilot and be timely and distinct from all other cockpit warnings.

Why is an auditory alarm necessary when the autopilot disengages?
Was there a particular accident where the pilots ignored visual warnings?

Yes, there have been several accidents caused when the autopilot has been inadvertently or automatically disconnected and the flight crew have failed to realise it happened. Even with the audible alert, it's reasonably common, but experiments in controlled conditions demonstrate that alerts provided in only one medium (just visual, or just auditory) are not reliably noticed in times of high workload.
Here's an interesting accident report I remember reading at the time, where the flight crew apparently failed to notice that they had deliberately disconnected the autopilot. For more on inattentional deafness, see the paper Failure to Detect Critical Auditory Alerts in the Cockpit: Evidence for Inattentional Deafness.

When I was flying RJs I always thought the worst of the audio alerts was the gear warning, which was a dual frequency steady tone, very much like the old test pattern sound when TV stations went off the air.  In sim training it was VERY easy for the sound the blend into background noise if you were becoming mentally saturated by an instructor piling on failure on top of failure.  The saving grace was the voice warning "Too Low - Gear" that came from the GPWS as you got lower.

Don't forget about Eastern Airlines 401 that crashed in the everglades. They were in a holding pattern and distracted when the captain inadvertently moved the control wheel which disconnected the AP.

@TomMcW: It didn't disconnect the autopilot, but, rather, caused it to downmode from altitude-hold mode (where the autopilot maintains the selected altitude) to control-wheel-steering mode (where the autopilot maintains whatever attitude the aircraft had when the yoke last returned to the neutral position).

@Sean: The fact is - the autopilot changed modes in response to an unintended input, without warning the pilots it was doing so... leading to the crash. Whether it changed modes as opposed to completely disconnecting is almost irrelevant.

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text:
Ducted Fan vs Open Propeller Efficiency
If we are talking about a slow flying aircraft with subsonic propeller tips, will adding a shroud increase efficiency, all else being the same?(ignoring the friction drag)

By ignoring the friction drag you remove the basis for a fair comparison. A friction-less shroud will help to increase thrust, but not efficiency.

Can you expand on that a bit? Why doesn't the efficiency increase, is it because of the added weight?

No, because of higher induced losses. The minimum is reached with fairly lightly loaded tips. Adding a duct will allow to load the tips more, so more thrust is generated, but disproportionally higher torque is required to keep the prop spinning.


text:
Which country would employ foreign air traffic controllers?
Air traffic controllers from Pakistan hold ICAO approved Licences (ATCL).
Which other country will accept this ATCL for employment acceptance?

As I know, Vietnam is one of the countries employing foreigners for the position of an air traffic controller.


text:
Do aircraft using only spoilerons for roll control, with no conventional ailerons, have a crossover airspeed?
Airplanes generally have a crossover airspeed (a minimum airspeed below which directional control of the airplane cannot be maintained in the event of a rudder hardover).  This is because, as airspeed decreases, the amount of lift generated by an airplane’s wings also decreases, forcing the airplane to fly at a higher angle of attack in order to maintain steady flight; this places the airplane’s wings closer to their stall angle, reducing the wings’ lift reserve, and, thereby, reducing the amount by which a lowered aileron can increase the lift of its attached wing, resulting in a reduction in the airplane’s maximum roll authority, while simultaneously increasing the rate at which drag increases with increasing angle of attack, and, hence, increasing the severity of the adverse yaw generated by the ailerons.1
However, not all airplanes use ailerons for roll control; some rely solely on spoilerons (spoilers used for roll control) on top of the wings.  To roll such an airplane, the spoileron on the downgoing wing is raised (reducing the amount of lift produced by said wing, and causing it to drop), while nothing happens on the upgoing wing.2  Notable examples of spoileron-only aircraft are the B-52G/H, whose long, thin wings would twist to an unacceptable degree under the torsional loads imposed by conventional ailerons (shortening the wing's fatigue life and risking flight-control reversal and/or structural failure of the wing), and the MU-2, which, in order to achieve good STOL performance, has large flaps along the entire length of its wings, leaving no room for conventional ailerons.
As a spoileron-only airplane’s roll control system does not depend on increasing the amount of lift produced by either wing, it should be immune to the decrease in roll authority at high attack angles that curses an aileron-equipped airplane with a crossover airspeed; thus, one would, theoretically, expect airplanes that do not use conventional ailerons for roll control, such as the B-52G/H or MU-2, to have no crossover airspeed.
Is this true?  If not, why?

1: This is aggravated by increasing the airplane’s vertical load factor beyond 1G, loading the airplane to its maximum allowable weight, and/or retracting the flaps (if any), all of which increase the angle of attack at which the airplane must fly in order to produce the amount of lift demanded of it, and, thus, increase the airplane’s crossover airspeed, or by retracting the leading-edge devices (if any) and/or flying with iced/insected wings, both of which decrease the wing’s stall angle, thereby increasing the airplane’s crossover airspeed; conversely, an aircraft’s crossover airspeed decreases if the nose is pushed over to maintain a vertical load factor below 1G, if the airplane is empty or very lightly loaded, if the flaps and slats/droops are fully extended, and the wings are clean of any contamination.
2: Most airplanes (other than very small ones) have, and use, spoilerons, due to their advantages at very low3 and very high4 airspeeds; however, the vast majority of those are also equipped with conventional ailerons.
3: As spoilerons do not increase the angle of attack of any part of either wing, they are unaffected by the reduction in lift reserve and increase in induced drag that come with higher attack angles.  Additionally, unlike conventional ailerons, they produce proverse rather than adverse yaw (as spoilerons increase drag on the downgoing wing [the one with the raised spoiler], rather than on the upgoing wing, as ailerons do); thus, for spoilerons, the yawing moment produced by roll-control-surface deflections assists with the intended manoeuvre, rather than partially cancelling it out.
4: As the aerodynamic force produced by spoileron deflection is applied at near midchord (instead of at the trailing edge of the wing, as is the case with ailerons), spoileron deflection places much lower torsional loads on the wing structure at very high airspeeds than aileron deflection does, reducing the amount of wing twisting (which reduces the aircraft's roll-control authority, shortens the fatigue life of the wing structure, and, at high enough airspeeds, can cause full-on control reversal and/or structural failure of the wing, all of which are generally considered to be undesirable) produced by roll-control-surface deflections.

I have never once heard of the term Crossover Airspeed.

@CarloFelicione  -- Crossover speed: "To further complicate the issue, the configuration and flight speed (flaps 1 and 190 knots) put the airplane in a flight regime where a fully deflected rudder would overpower the lateral control system. This phenomenon came to be identified as the "crossover speed," or the speed at which the lateral control system (ailerons and roll spoilers) could exactly balance the available full rudder deflection. "  From FAA accident overview: https://lessonslearned.faa.gov/ll_main.cfm?TabID=4&LLID=1&LLTypeID=2 .  Google "crossover speed" for more.

No, the Mitsubishi did not publish a crossover airspeed.

It seems the question does not specify level flight.  Since the deployed spoiler makes a net decrease in lift coefficient, and net increase in drag coefficient, of the whole wing system, there is surely some power setting below which altitude cannot be maintained with the rudder hard over, but I guess that's not really an answer.

I don't think it can be answered in a general way, as edited. As you explain, there shouldn't be, but we can imagine a situation when it would be so (for example, spoilerons' actuators unable to drive at very high airspeed). But any sensible design would put such conditions outside of the flight envelope. How can we then assess if the aircraft is prone to such crossover if the conditions are limited by other factors (and thus probably not even tested for)?

Have you seen the rudder on the B-52G/H? Won't take much to overcome a hard over of that tab. ;)

You could shorten the question to "Are ailerons or spoilerons able to counter a fully deflected rudder on the whole flight envelope of any aircraft?"

FWIW, the EA-6B I flew in the Navy used spoilers, (spoilerons?  We actually called them "flaperons" but they were spoilers...) but there was not a crossover airspeed or AoA.

Having personally flown onboard a 737 during experimental flight testing of simulated rudder hardovers (and performed post-test analysis) I can assure you, it’s not a question of the roll effector details. So, the short answer is “not necessarily.”
First, just to clarify and correct the inconsistency, crossover refers to the lateral (not directional) balance, primarly between rolling moment due to sideslip and lateral control inputs. Depending on the state of the aircraft there are also dynamic terms that come into play, mainly rolling moment due to roll rate and yaw rate. Primary variables that feed into the static terms are angle-of-attack (AoA), flap setting, and even engine thrust somewhat. Beyond a certain level of AoA on many configurations, the magnitude of rolling moment available (from full lateral control input) decreases more rapidly than other rolling moment terms.
So, the key is whether that ‘crossover’ AoA is in or outside of your normal operating envelope for a given configuration. Spoileron-only aircraft may still have a crossover speed but it’s not likely to be reached in normal operations and it depends on other details as well. For example, is maximum rudder deflection a function of speed, how effective is the rudder, what flap setting, how long of a delay from rudder input to countering lateral control input?
In other words, a blanket statement of "if an aircraft has only spoilers for roll control, then there will be no crossover speed" is not true.

The MU-2 flight manual makes no mention of any crossover airspeed. I suppose that's because of the excellent control authority of the spoilerons.
I think you mean Vmc/Vmca or Minimum Controllable Airspeed (I've seen it abbreviated both ways). I've never heard of the term "crossover airspeed."
All multi-engine airplanes (except those like the Cessna Skymaster where the engines arranged in a push-pull configuration along the center longitudinal axis) are tested to determine this airspeed during certification test flights. Vmc is designated on the airspeed indicator as a red radial line over the white arc that indicates when it is safe to extend and operate the flaps. (There is another red line that indicates Vne or Never Exceed airspeed).
This should never be confused with the blue radial line that makes Vyse, or best single engine climb airspeed.
Vmc is determined by the manufacturer as the minimum airspeed at which it's possible to recover directional control of the airplane within 20 degrees heading change and, thereafter, maintain straight flight, with not more than 5 degrees of bank, if one engine fails suddenly with:

Take-off power on both engines
Rearmost allowable center of gravity
Flaps in takeoff position
Landing gear retracted
Propeller windmilling in takeoff pitch configuration (or feathered if automatically featherable)

On the Mitsubishi MU-2 Vmc is between 89 and 100 (knots calibrated airspeed) depending on how the aircraft is configured at any given moment.

No, that's not what I'm referring to.  The crossover airspeed is the airspeed below which the maximum roll authority from the airplane's lateral controls is less than the sideslip-induced rolling moment from a fully-deflected rudder, as explained in the question that my question links to the answer to.

On a side note (it isn't what the question is about either way), the longer abbreviation Vmca means minimum control speed in the air speed, and is used in contrast to Vmcg, the minimum control speed on the ground.

I can see what you're getting at, your point is essentially, if a pilot deflected the rudder to its fullest extent, is there a minimum airspeed at which it could be overcome by aileron or spoileron control?  But I seriously doubt that aircraft manufacturers test this phenomena, in any event I have never come across the term in 38 years of aviation. A hard over rudder at any airspeed in anything other than a fully aerobatic airplane is going to cause a lot of grief. American Airlines flight 587 was an example of what would happen to an airliner if full rudder deflection is commanded. Airplanes are indeed tested for Vmca as mentioned above.
At the same time can mention that in many light aircraft one could perform a sideslip maneuver with full rudder and aileron input in order to lose height rapidly and indeed, this maneuver was used in the Air Canada Flight 143 emergency as well as TACA flight 110. However it is highly doubtful that manufacturers have ever published a "crossover airspeed".

AA587 is not a good example, since the overstressing of vertical stabilizer was a dynamic effect caused by quickly alternating between left and right command, not just keeping the rudder at the stop. A better examples would be United Airlines 585 and USAir 427, where full rudder deflection was a result of the actuator fault (both crashes) and Northwest Airlines 85, which landed safely, but a 747 has a split rudder and only half of it locked up in the extreme deflected position while pilots kept the other deflected the other way to compensate.

It might not be good to trust an aileron or a spoileron at high AOA.
To start, "minumum cross over speed" is the minumum airspeed at which an aircraft has sufficient roll authority to create an opposite sideslip to a rudder hard over.  Slipping in the opposite direction puts side force on the horizontal stabilizer, helping counter act the rudder force.
The difficulty with ailerons at higher angles of attack are as follows, the downward aileron creates drag on the same side as the rudder, creating an "anti-coordinated" condition (it makes the yaw worse). Also, at high AOA, the wing tip may stall, adding to the woes.  On the other side, the upward raised aileron at high AOA is blocked from the airstream by the wing, reducing its effectiveness.  A spoileron, though slightly safer, would have similar issues.
One solution, particularly with airliners blessed with plenty of available thrust, would be to use a clamshell on the opposite wing to hold straight.  And, eventually, as on a hypothetical B-52 I,  get rid of the vertical stabilizer/rudder and just use the clamshells.
With the current BUFF, differential thrust is also an option.


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Why can a localiser be used without a glideslope, but not vice versa?
An ILS consists, at its most basic, of two components: a localiser (to provide lateral guidance) and a glideslope (to provide vertical guidance).  The two are typically used together, for an ILS approach, but the localiser can also be used on its own, for a localiser-only, or simply localiser (LOC for short), approach (for instance, if the glideslope is inoperative or nonexistent, the aircraft lacks a functioning glideslope receiver, or the pilot is shooting a back-course approach).  For a localiser-only approach, the pilot uses a specified series of navigational fixes to mark off each segment of the approach; each of these segments has a specified minimum safe altitude (which is shown on the approach plate), and the pilot uses this information, and their onboard baroaltimeter, to maintain terrain clearance during the approach.
While localiser-sans-glideslope approaches are quite common, there are, to the best of my knowledge (feel free to correct me if I'm mistaken here), no examples of the reverse: a glideslope-sans-localiser approach, where the pilot uses the glideslope for vertical guidance but relies on ground- or satellite-based navigation fixes for lateral guidance.
What allows the use for an approach of a localiser without a glideslope, but not a glideslope without a localiser?

In a nutshell, roughly speaking, when the localizer needle comes alive, you know where you are laterally with respect to the final approach course. When the glideslope needle comes alive you know where you are with respect to your height above the runway. If you followed the glideslope absent lateral guidance, you could well let down into an obstacle well off to the side of the localizer. Others I am sure will provide detailed parameters.

Because there would be no benefit to doing so.

where the pilot uses the glideslope for vertical guidance but relies on ground- or satellite-based navigation fixes for lateral guidance.

As you correctly point out, if using only a glideslope, the pilot would have to rely on other navigation facilities for the horizontal guidance, for example a locator/NDB or RNAV. But if a locator/NDB or RNAV approach is available, the pilot could just use that approach for the vertical guidance as well.
For an NDB approach, there is no actual vertical guidance, but the pilot will descend manually, typically while cross checking distance to threshold using a DME. This is relatively inaccurate, so an NDB approach typically has a relatively high minimum descend altitude (the altitude at which the pilot must visually see the runway in order to continue).
The reason an ILS approach (LOC+GP) generally has lower minima is because a LOC and GP combined is very accurate. If you were to combine an NDB with a GP instead, you would still have accurate vertical guidance, but not very accurate lateral guidance. Because of this, it would probably not be possible to define lower minima compared to a NDB/DME approach. What good would a lower minima do you, if, by the time you reached, say, 200ft, you find out that you are not actually aligned with the runway, because the lateral guidance is so inaccurate? So even with accurate vertical guidance, you would need time to align with the runway once you get below the ceiling, which means our theoretical NDB+GP approach would need minima similar to that of a pure NDB approach. Hence, there isn't really anything to be gained.

I disagree that there would be no benefit to doing so. One specific instance would be flying a visual approach using the glideslope for VNAV guidance. Under FAA regulations (§91.129) large or turbine-powered airplanes are required to follow the glideslope, where provided. This is consistent with stabilized approach criteria, and aids the pilot in flying more precisely.

@JWalters Out of curiosity, if flying a visual approach, how can the pilot be sure the glideslope is switched on?

I would not. I can fly a visual approach without any instrument aid, so a glideslope indication, if received, could be verified by cross checking altitude and position, just as it would in an actual instrument approach to verify not receiving a false lobe. That being said, the above is theoretical. In actual practice if any portion of the ILS was NOTAMed out of service I would nearly always be able to resort to an RNAV approach for guidance on a visual approach.

Beyond those listed factors, I would suspect that in many areas only a relatively narrow slice of the space where a glide slope could be detected would have any kind of meaningful shape.  Depending upon shape of terrain to the side of the runway, a plane that isn't centered horizontally in the glide slope beam might receive a "glide slope" which which slopes up or down at a completely meaningless angle.

Let's consider the ILS on its own, with no supplement navigation aids like RNAV / GPS. Assume IFR conditions.

A LOC+GS approach can get you onto the runway.
A LOC-only approach simply won't work, you need at least one more piece of information, e.g. DME.
A LOC+DME approach would be similar to a VOR+DME approach. You'd step down your altitude as your DME reading decreases. At the end you either see the runway well enough to switch to visual, or execute a missed approach.
A GS-only approach provides no information whether you are on the extended runway centerline. If you follow the GS all the way down, you would crash into something, e.g. the hangar or the planes on a nearby taxiway.

For the same reason, when flying an ILS approach, you should capture the localizer first, then the glideslope; never the other way around.
So we must pair GS with some other navigation aid, if LOC is unavailable. But what?

You cannot pair GS+DME. GS+altimeter already gives you a DME of sort.
If you have RNAV, might as well go completely RNAV anyway.
VOR+GS works, provided that the aircraft have two nav radios. Tuning directly to the GS channel is possible with the existing hardware, but the cockpit controls and displays are not designed to do that at the moment.
NDB+GS would also work, but with a lower accuracy.

However, as pointed out above, the danger of misplacing the aircraft horizontally is greater than vertically. A VOR+GS would have relatively inaccurate lateral guidance, especially at long distances, making the accurate signal of the GS useless in improving the minimum altitude of the approach.

Couldn't DME from a navaid off to the side of the approach course be used for lateral guidance?

@Sean no, because that'll tell you you're on a circle around the DME, but it doesn't tell you which point on the circle is it. Furthermore the distance (radius of the circle) keeps changing unless the DME is along the extended centerline. You can use two DMEs to get an exact fix, provided that you can do the math quick enough. That's what the RNAV computer is doing.


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Can the landing gear be pulled up while the plane is on the ground?
If a pilot makes a mistake and inadvertently touches the gear up lever, will it actually activate while on the ground and make the plane drop onto its belly?
I suppose that there would be some sensor to prevent this, but I would like clarification on that.

On 747-100/200 aircraft there's a sensor setup that determines whether the aircraft is on the ground. When the sensor says the aircraft is on the ground, a metal flange is positioned in the vertical slot that the gear handle must move through to raise the gear. The flange physically prevents upward movement of the gear handle. When you take off, you can hear the flange retract when the gear is off the ground, and you can then move the gear handle up through it's vertical slot.

Probably a duplicate of: How does the squat switch work? but the existing answer could be improved easily. A search on "squat switch" retrieves good images, like this one, cited in a comment of the linked answer.

Well. The term squat switch is self explanatory. Thanks

Without interlocks, raising the landing gear on the ground was an important plot point in Nevile Shute's novel "No Highway". This could be written off as artistic licence, except that his "day job" was aircraft design.

I recall a story of a fighter pilot who accidentally landed with gear retracted and then tried to cover up his mistake by flipping the switch on the ground- unfortunately for him there was enough pressure remaining in the hydraulics to cause the aircraft to lurch up on the gear. Probably 1970s give or take a decade or two.

@SpehroPefhany - somehow I doubt very much that landing a fighter, or any aircraft, with the gear retracted could be "covered up" by putting the gear down once all the excitement had subsided.

@BobJarvis The idea being that the pilot could claim he was not at fault because the gear failed to deploy, of course.

This just makes me think of the time where Homer Simpson did exactly this - "I keep telling you I'm not a pilot!" "And I keep telling you, you flyboys crack me up!"

@SpehroPefhany I can't imagine a military pilot, or any pilot for that matter, not being acutely aware that the FDR would always tell the true story.  I don't doubt that you recall this story... I'm just not so sure I'm ready to believe that it's true.

@J Way out of my area of expertise, but I don't think all F-111-era or earlier military planes had much in the way of flight data recorders. Of course it's possible the story (in Popular Science or whatever it was) was inaccurate and/or anecdotal. In any case, a failure analysis would have shown there was nothing wrong with the aircraft so the point is valid.

The following link shows a fighter plane gear retracting DURING takeoff, resulting in a long slide.  However, I don't know if it was mechanical failure or pilot error.  https://www.youtube.com/watch?v=-Cunaek9W24

I've heard of a show-off pilot ordering the gear up before taking off, trusting the switch to not actually pull it up until after takeoff.  (The idea was to pull it up the instant the plane was airborne.)  Unfortunately, there was a little hump in the runway...

I used to work at an aircraft works, and we could watch the pilots taking off and landing. Once a test pilot was practicing take off, wheels up, loop round, wheels down, land and roll, take off... of course the time came when he forgot to put the wheels down and just slid along the ground. We looked at each other and said "well, there went our Christmas bonus."

Anecdotally, I have heard of a Delta 727 that allegedly had this happen during maintenance. As I understand the situation, power had been removed from the aircraft and in that timeframe the gear handle was raised to perform some sort of maintenance check. The handle wasn't tagged out, neither was power, and another mechanic came into the cockpit, turned power on and immediately turned on hydraulic pumps. I've heard that story told a few times from different people but don't know if it's actually true.

There is a weight sensor which senses if the plane is on the ground. This sensor prevents gear retraction while the plane is still on the ground. Failure of this sensor would prevent gear retraction after takeoff.
If you note closely, the landing gears (even the non-retractable ones) are not connected using a simple metal pole; rather, there is an oleo strut which is compressed by the weight of the aircraft. Besides airborne / ground detection, the struts absorb the vertical energy during touchdown.

I recall some decades ago engineers experimented obtaining the plane's gross weight by installing weight scales to each landing gear (as opposed to just an air/ground detection). The readings were found to be inaccurate and they soon abandoned the idea.

Landing gear stories cannot be complete without mentioning this incident in 1990:
A training captain of a Saab 340 was betting with his students that the weight-on-gear mechanism would prevent gear retraction while on the ground. On the accident airplane type, the mechanism would lock the gear handle, but the lock can be overridden if the pilot manually pull out and move the handle. The instructor confidently pulled out the handle and to his surprise, the hydraulics started to move and the gears were retracted while the plane was still on the ground.

(image source)
The aircraft was written off. This incompetent instructor pilot was killed 11 years later in another accident.

I wouldn't call the Saab pilot incompetent on the basis of the totaled 340 alone. My curiosity has done damage to lots of equipment, and I encourage that same curiosity in my children. Imagine the look on his face when the gear started retracting!

@mins: As a software developer, I would file that under "Things nobody ever considered might happen, not even QA". Automated and dynamic smart test suites might catch those issues in software and CAD today, as they can dynamically explore all the code and component paths. But on a mechanical system designed in the late 70's and early 80's, I can see how it slipped through.

@dotancohen Despite the training captain's vast experience and reputation, his competence was quickly brought to question after the deadly accident of Crossair 3597. Throughout his career he has failed multiple checks and examinations even after repeated attempts, and graded "below average" on many occasions.

@kevin: That brings the competence of his superiors into question as much as his own. Who let him hold the stick with that many issues?

@dotancohen you're encouraged to read the final report of the crash to find out more (= You may start at page 20.

It is possible to override this mechanism (at least on some planes - I'm no expert, just remember this from working on simulation for aircraft repair), which is sometimes done when servicing the landing gear.  Needless to say, the plane should be placed on servicing jacks first.  Jacking up a plane (especially a large one) is no small task - on the ones I was working with it can take most of a day - so it is not a common procedure.

@mins That capability would almost certainly be needed for maintenance. Even in maintenance, though, they shouldn't need to retract while the squat switch is in the ground position (I'd assume the jacks lift the gear off the ground before any attempt is made to retract the gear, since otherwise the tires would be damaged.) Also, a condition that prevents the gear from retracting while the engines aren't running could be a problem in the case of something like US Air 1549.

@reirab: No offense, but a car hood is also required to open for maintenance, but it cannot be opened while driving, even if I pull on the opening lever, there is a security. Considering the price of an aircraft... this makes me think sometimes aviation is incomprehensibly archaic, just like for voice/data recorders and their ridiculous ULB, compared to the cost of recent SAR operations.

@mins " it cannot be opened while driving" - don't bet your own money on that. https://www.youtube.com/watch?v=JA9piRHcQUE (and you can easily find more video evidence).

@mins That's why I said the squat switch would still be a reasonable mechanism for a lockout. Just not the engines running. You generally don't want the engines running when you're doing maintenance on the landing gear... especially wing-mounted jet engines. But, yes, much of aviation technology is indeed quite a bit older than the technology in most cars. There are two main reasons for this: getting any kind of changes designed and certified for an aircraft is very expensive and most aircraft are simply much older than most cars.

@mins: Car hoods can open while driving.  I've had it happen to me.  Though I'm surprised that the hydraulics can produce enough force to pull the main gear sideways while the weight is on the wheels.

@jamesqf and afephzero: This shouldn't be possible on cars sold in France (and probably in the EU), there is a security on the hood itself that must be operated manually (so you need to do two actions in that order: In the car pull up the lever, then go to the front and release another lever. I never heard of a default.

Another Re: Car hoods - I left mine open, but with the safety catch latched. Two miles down the road at 50 MPH the safety catch was not enough. I was very, very confused. And now I'm paranoid about it happening again so I driving down the road I always look at the end of the hood to see if it's popped up at all.

@mins: Yes, the safety catch is supposed to prevent the hood from opening while driving, but it doesn't always work.  Like the squat switch is supposed to prevent the gear from operating while there's weight on wheels...

@jamesqf: "it doesn't always work", for me it works and I see no reason it would be faulty. Sorry but I can't buy the hood that opens while driving if nobody tampered with it. This hood story is just an illustration of whether gear retraction process can be improved, I think everyone interested has got the picture. Of course cabin doors can open in flight, and fuel tanks can leak, everything can fail exceptionally, and in this case corrective actions are required.

It's sort of interesting that the Saab 340 was written off. In the picture, it looks like it settled down nicely. I wonder what the damage was and why it couldn't be economically fixed. Was the structure compromised just by its weight resting on solid ground like that?

@Dronz: You may ask this question in a separate post (but ensure you do not ask for opinions but facts)

@dronz I doubt the aircraft "settled down nicely.' It wasn't landing at the time. Most likely it tipped to one side or the other in the process (think what happens when someone walking with two crutches loses traction and falls) and damaged one or both wings, or key portions of the airframe, landing gear mounts or maybe even the wing spars to the point where the aircraft was not economically repairable.

@mins "I see no reason why it would be faulty." Um... What? A fault means something is wrong with it. Anything can foul up and make a situation go sideways. Nothing is perfect.

@T.J.L. With due respect, the well-worn risk zero doesn't exist is an obviousness nobody will challenge. It's true an aircraft engine will eventually land in my garden if time is not counted. In reality, the chance such event can happen within a lifetime is quasi-null, it's acceptable to say "I see no reason why it would fail".

@mins "I see no reason" and "It is not likely" are two entirely different statements.

@T.J.L.: Ah I see, then let's say, "I see no statistically significant possibility for it to fail"

The only question still left: did The Simpsons actually inspired this bet, or vice versa did they hear about the incident and put it in the show?

This incident was "half on ground" during takeoff:
Last year, the copilot of a Dash 8 applied erroneously the gear lever during takeoff as the rear gear had still ground contact. This resulted in a tail strike. The aircraft bounced back on runway 9 of Saarbrücken's airport, slipped some hundred meters and will be written off as well.
See the report of the German aviation authority (English Edition of The Report), pages 60-76. It turns out that the Dash 8 has a weight-on-wheels sensor only on the front gear. The report says that the design responsible called this to "comply with the design logic".
Differently from the incident @kevin mentioned, the gear doors were already closed as the fuselage touched ground.

This makes you wonder if the designers ever saw a plane take off. You'd expect that the landing gear designers would know which wheels land first and take off last.

@MSalters, I think this falls under dotancohen's comment on kevin's answer - nobody in design or QA thought of the possibility of that during test. They are humans, after all...

@FreeMan: Reviewing engineering plans is a learned skill. If I review a fellow engineer's idea for a squat sensor on one wheel, I know what failure mode it's tyring to prevent: "retract gear while there is still weight on the gear". I then ask myself, "what does fail mean in this context?" The answer would be that there is still weight on the gear, and yet it's retracted. How can that happen? The weight isn't on the front wheel with the sensor. Then it follows the weight is on the other wheels. When is the plane on its rear wheels? At takeoff. So what happens if I then retract the gear? Oops

I'm not some sort of supergenius, but I know there are two general failure modes for any mechanism: Type I, not working when you're supposed to work, and Type II, working when you are not supposed to.  Sometimes, one mode is much less important than the other (and, without knowing much about planes, I would guess it's better to refuse to retract than to retract wrongly), but if one of them doesn't matter at all, make a mechanism that never does anything or always does something.  @MSalters chain of reason strikes me as obvious and obviously correct.

@Malvolio: There's also a generally nasty case of "stuck half way" which you need to consider. E.g. gear retracted, but gear bay doors refuse to close. Or worse: gear started to fold, and cannot carry the planes weight anymore, but did not full retract. The squat switch is supposed to be binary, but real physics tend to be analog. What if the sensor shorts out and doesn't give a reading? And since it's close to a wheel, what if the wheel/brake catches fire? It would be quite dangerous if you have a fire and then have the gear collapse. As a QA engineer you have to consider everything.

@MSalters, I'm a programmer not an aeronautical engineer, so the problems of analog don't come up in my own life, but a friend of mine is a private pilot and once found himself in exactly the situation you describe: one gear wheel partially retracted, neither a gear-down nor gear-up landing was possible.  His solution was to open the door (in flight!) and snag the dangling wheel with the tow-handle and pull it the rest of the way up.  After that, it engaged properly and would lower and lock in place.

@Malvolio programmers may not have to deal with analog situations that much, but nondeterminism can crop up in the most unlikely of places... https://gcc.gnu.org/bugzilla/show_bug.cgi?id=323#c43

Safety standards have improved since the 1940s, but soon after a £1m restoration project on a WWII Spitfire, somebody blocked the runway at a local airport by demonstrating this design flaw. Apparently the pilot got confused about which of two levers retracted the flaps, and which retracted the landing gear.
The accident happened just before sunset, so I don't think there are any good pictures available on the web that show the damage.
http://www.bbc.co.uk/news/uk-england-leicestershire-22474805
https://assets.digital.cabinet-office.gov.uk/media/5422ed3640f0b6134200014f/Vickers_Supermarine_Spitfire_MK_XIX__G-RRGN_5-2013.pdf

So THAT's why the gear lever has a wheel on the end of it!

@TomMcW Well, you have half an excuse for not knowing your right hand from your left when flying that particular Spit. It has a Griffon engine instead of the more common Merlin, so the prop rotates the opposite way from what you might expect.

authors: Bob Jarvis - Слава Україні


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Questions regarding Non-precision Localiser approach (KSEE LOC-D Approach)
Scenario
Say we are doing some practice approaches into KSEE on the LOC-D approach. We are just southwest of the field and ATC/CFII says to climb to 5500 direct to BARET, cross BARET 5500 cleared for the localizer approach. So we climb to 5500 direct to BARET. We fly direct to BARET on Magenta needles. Once we get over BARET (Established outbound) we switch from Magenta to green needles for the loc-d approach and we fly our procedure turn to 134 heading for 1 minute outbound. Once the minute is up, we turn left heading of 314 to intercept the localiser course.
My questions
#1 This would put us between WOPOS and BARET under the IAP published altitudes (WOPOS is 6800 and BARET is 5900), since we have been at 5500 since crossing BARET. Would we just maintain this altitude until crossing BARET for ZIRLU which is 4900. Does the updated 'clearance' of 5500 trump over the published altitudes?
#2 can we use GPS (magenta needles) to fly the published missed to the VOR?

You should never get this clearance, and should reject it if you did. The procedure turn takes you close to peaks that are nearly 5000 feet. 5500 feet is a clearly inadequate altitude.
You can fly the missed approach with an approved GPS.

Even if it was a practice clearance for a practice approach from a DPE/CFII? My DPE gave me this while VFR during my checkride acting as ATC for my ride. Ok, thanks for clarifying the missed with GPS!

@TrevorMiller I'm not sure it's helpful to ask students to fly practice approaches in ways they never would in real life! And even VFR with a CFII watching that's pretty darn low over mountainous terrain! On a cold day you might actually hit a mountain!

Hey Chris, I updated my comment on the situation! I agree 100% with you, this just happened to me and I was confused. I believe I was left so low because of the Bravo from 5800 to 10000

@TrevorMiller Seems likely. I'd not worry about it too much. If it was your CFII I'd suggest you have a talk with them about briefing things more carefully when they are deviations from realistic IFR flight. Congratulations (I hope) on your instrument rating!

Roger that and thank you!! I appreciate the insight

one quick question! The lod/dme freq 110.5 has an underline to it. Does that mean it doesn't have morse code to identify it?

@TrevorMiller Not quite. It means there is no voice on the frequency. Some navaids you can do voice communications over the frequency.

So if I was flying to KSEE about to fly this approach (LOC-D) and I had the frequency on and I check it with the nav function, it should or shouldn't have a morse code? Trying to understand what No voice means for the approach! Thanks for the quick response as well

@TrevorMiller It should have a morse code. No voice means as it sounds- nobody can verbally talk to you on the frequency.

Roger that thanks Chris!


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Has the United States Air Force used Contra-rotating Propeller Aircraft?
I recently saw a picture of a Russian Bear(TU-95) intercepting one of our(US) military aircraft over the Pacific Ocean.
Many years ago, when I flew in reconnaissance aircraft, we were frequently intercepted by Bears which surprisingly flew at 500+ mph airspeed.
Yet no US Military Aircraft uses contra-rotating props(to my knowledge).
Why is that?

In short, the US didn't need one.
The main reason for the development of Tu-95 was the rather unique situation existing after WWII, when the Soviet Union needed a heavy bomber to carry the (then very heavy) nuclear weapons. Due to the lack of bases anywhere near contiguous United States, the Soviets were at a significant disadvantage when it came to nuking the US before the ICBMs came into picture (US had bases in Europe and in Pacific). At that time, heavy bombers were the only way to deliver a nuclear payload and it required the aircraft to be fast, have a intercontinental range and be able to carry a reasonable payload.
The first attempt in developing a long range bomber during the last days of WWII by the Soviets didn't work out and as a result, they simply reverse engineered USAAF B-29s which had 'landed' in Russia into the Tu-4 'Bull', which lacked the necessary range. In a way, the B-29 was the forefather of Tu-95. Further development continued on this airframe, culminating in the Tu-80 'Barge', which had the necessary range, but was considered unsuitable as it lacked speed, which would be fatal against jet interceptors.
The Tu-95 was developed at the same time of the B-52 'stratofortress'. Actually the Soviet Air Force preferred the jet powered Myasishchev M-4 and Tupolev had to convince Stalin about the Tu-95's suitability. During the initial design phase, the Tupolev bureau considered two versions- one with four turbojets and another one with turboprops. The turbojet version was discarded as it would've lacked range due to the fuel hungry turbojets (Tupolev turned out to be right about that as the M-4 was sidelined due to lack of range).
The payload and speed requirements required a very powerful engine (the Kuznetsov NK-12 is the most powerful turboshaft engine ever) and the contra-rotating props were selected to overcome the problems associated with the large diameter of the propellers.
Western countries also did a lot work with contra-rotating props, but the advent of jet engines and the complexites associated with the counter-rotating props meant few graduated from the prototype stage. The Huges XF-11, for example had counter rotating props initially; they were changed to conventional ones after Huges crashed in it. The Fairey Gannet and Avro Shackleton were among the few western contra-rotating aircraft to see regular service (both were used in ASw roles, which highlight the increased endurance offered by them). A number of contra-rotating aircraft were tested during the end of WWII, but the advent of jet engines meant that the required speed could be achieved in a far better way.

Also Soviet engines were less efficient due to lower precision of manufacturing, which exacerbated the problems achieving sufficient range.

If you consider the military version of the Cessna 337, the O-2, this [cool looking] aircraft has two separate motors that spin props in opposite directions (aka contra-rotating). It is called a coaxial twin.

@Pugz, I don't think that qualifies as contra-rotating. They are not coaxial, so they are only counter-rotating.

@aerolias Excellent answer-I always thought it was because they couldn't shut down(feather an engine) in flight; unlike standard turboprops. What I was amazed by is the fact they still use them.

@JanHudec oh sorry, I meant centerline thrust twin, not coaxial. Oops :-)

There were a couple attempts (Douglas Mixmaster, Hughes XF-11) at same, but none of them ever made it to serial production.
The Mixmaster, though fast, arrived at the dawn of the jet age and wasn't fast enough to compete with jets.  The Air Force transitioned to jets pretty quickly.
The Hughes developed hydraulic problems it's first flight and crashed, nearly killing the pilot (Howard Hughes).  Again, fast but not faster than jets.
The Soviets spent a lot more time developing that tech because they had extensive experience with turboprops (they were still flying turboprop airliners long after US / Western carriers had transitioned to jets) and early, Soviet jet engines were very inefficient.  Not having quite the budget of the USAF, they needed something fast yet fuel efficient.  Contra-rotating props gave them speed while turboprops gave them efficiency.

Contra rotating props are mechanically complex and pose serious maintenance issues when used on piston engines, and tend to be very noisy. The advantages are counterbalancing of torque, and more thrust in a smaller space than a single prop. However, the rear prop will not have the smooth airflow the front prop encounters - it will be cutting into the pulsing airstream from the front prop, so additional stress is imposed.
Several military aircraft in the US tried them in the prototype stage but abandoned them when the drawbacks outweighed the advantages. These include the Northrop XB35, which had gone to single props in the YB35 production version, before the turbojet variant, the XB-49 eliminated propellers. The Hughes XF-11 abandoned contra rotating props in its final version. Another Northrop design with contra rotating props was the XP56, although its contra rotating props were but one of many problems that design had.
The Avro Shackleton, which was successful, was known for high maintenance on it's prop gears.
A notorious example was the XF84H"Thunderscreech", infamous for its very high noise levels... just like the TU-95. The advantages of contra rotating props were not found to outweigh the disadvantages.
Later western military turboprop designs, such as the Lockheed C130, dispensed with the complexity of contra rotating props in favor of better single prop design. Same is true of the Airbus A400 military transport - four single props.
Contra rotating props were part of the Unducted Fan design, which saw some use in the Soviet Union, but didn't prove to be advantageous enough to see commercial use in the US, due partially to high noise that would have had problems with noise restrictions at most western airports. Ironically, some of the prop blade tech developed for the GE CFM36 unducted fan was later used on the huge and highly successful GE90 turbofan.
In the end, the western nations solved the issue with the high bypass turbofan, which is equally efficient, capable of higher speeds, and produces far less noise.
If anything, the TU-95 stands as a testament to the Russian ability to build robust military platforms, and a testament to western tech to solve problems with a different design rather than brute force.

The US Air Force used the OV-10 Bronco during Vietnam. It had twin turboprop engines. The props counterrotated by using an extra gear in one of the engines to make it spin in the opposite direction from the other prop.
Although the OV-10 was ostensibly an observation aircraft, it carried some serious firepower, such as rockets and miniguns. It was also capable of carrying a small complement of passengers, for either inserting a special ops group or exfiltrating wounded personnel.
I don't know if the Air Force still has any on active service, but they are still flying in other places.
It seems to me that I read that they might be used in a similar role as the A-10, when the A-10, which is more expensive to operate would be, ahem, overkill.

That is not what OP means. They refer to two propellers on ome engine shaft, turning in opposite direction. The Bear has four sets of these, 8 propellers in total.

Howard Hughes was developing such a system. He crashed and was seriously hurt. He never built another aircraft with this propeller arrangement. It turned out that a single O-ring had failed. I can see the advantage of this kind of arrangement, but I suspect it results in a very heavy and complex propeller system.


text:
What are the limitations of using a single shaft between the compressor and turbine in a jet engine?
Question Background
I'm studying the internal structure and components of a turbojet. I can see there is a shaft between the compressor and the turbine, so that energy is mechanically extracted from the exiting gas and used to help the compressor rotate. You can appreciate it in the next image:

Question
I understand the shaft is there so that the turbine helps the compressor move. But this introduces a serious constraint: both the compressor and the turbine need to rotate at the same speed. Is this true in general? How is this managed when there are several shafts connecting several compressors/turbines? Are reduction boxes needed here or do they, in fact, move at the same speed? Is this a big deal, does it introduce any serious limitation/drawbacks regarding the exiting air power?
Just started studying jets, hope the answers are not very trivial.

This answer explains multiple shafts. I'm sure there are others lurking around here.

"used to help the compressor rotate" - No, no, no - not 'help' - the shaft is essential to forcing the compressor to rotate.

How is this managed when there are several shafts connecting several compressors/turbines?

The different shaft will rotate at different speed from each other, but the relative compressor/turbine pairs will rotate at the same speed.
Expanding a little, in the most complex case that I heard of, there are 3 shafts: High Pressure (HP), Intermediate-Pressure (IP) and Low Pressure (LP)

Image source
HP turbine and HP compressor will rotate at the same speed, but this is not necessarily equal (in fact is highly likely that it will be different, otherwise there would not be the need for different shafts) to the speed of the IP compressor/turbine couple. And this will be different also from the speed of the LP turbine/fan couple.

Are reduction boxes needed here or do they, in fact, move at the same speed?

They generally rotate at the same speed. And generally you don't want gear boxes in the central section of your engine. Apart from the maintenance nightmare that they would become, given the rotational speeds and energies involved, they would be extremely heavy, inefficient and would constitute a critical system quite prone to failure.
An exception are the fans, they have enough space and are in front of all the rest of the engine, allowing the housing of a gearbox within their enclosure. You can find a better discussion about this case in this question; keep in mind that here you have 3 compressor stages with only 2 turbine stages, the gearbox was necessary to have a speed differential between fan and IP compressor without requiring 3 turbine stages and an additional shaft. (thanks to @fooot for pointing the PW1000G out)

Is this a big deal, does it introduce any serious limitation/drawbacks regarding the exiting air power?

As everything in engineering, there are trade-offs. The ideal performance would be obtained via an infinite set of infinitesimally thin turbines/compressors, each rotating at a slightly different speed, but this is not technologically feasible. The engine designers will then settle for a slightly sub-optimal performance, but it will be actually achievable with 1 or 2 (3 in extreme cases) discrete shafts.

I wasn't expecting such a detailed answer. Thanks.

@fooot I was wrongly focusing on the intermediate section. I will add that to my answer.

@fooot If you mean PW1000G are only GTF on any airliner so far, that not correct. There are a few examples from past. Most notables are Garrette TFE731 (total >11000 built) and Lycoming ALF 502. But they are smaller engines and PW1000G series is the first in medium thrust class with High BPR. Looks like RR UltraFan will be the first one in the large thrust class.


text:
Why might an airliner fly a large U-turn before landing?
I was on a flight1 from San Antonio, TX to Toronto and, when arriving in Toronto, the plane went quite a way past the airport, made a big U-turn, and then landed. We were coming from the west.
I thought it might have been a need to adjust for the runway, but as I said, we went quite a way past the airport, meaning after the turn we had to fly "a little bit to get back to the airport". All that even before starting the process of descending for landing (if it was just a matter of adjusting the direction for the runway, what would be the need to keep the high altitude and go so far to make the U-turn?).
Does anyone know the reason? It seems that some flights coming from the west do that move.

Air Canada 7722, October 8, 2017 (history will not persist)
(flightradar24.com) Image shows the flight's route with a final left U-turn prior to landing.

Could be a lot of things, most likely they had to enter the traffic flow, so they had to fly out and then get in line behind somebody on a long final. You can't just jump in the middle because there are spacing requirements.

Ask yourself what is the alternative; should some planes land from the west end while other planes are landing from the east end of the runway? What could go wrong? If nothing goes wrong on the runway, what could go wrong on the taxiway?

See http://www.faraim.org/aim/aim-4-03-14-187.html

I live near an airport and often take my kids to watch takeoffs/landings.  From my experience, the answer to @EricLippert question seems obvious.  They take off one after another.  In your airplane seat you don't realize there are other planes, but from my picnic bench (just outside the restricted runway area) there is a clear queue of planes.and it is obviously better if everyone was going the same way.

Pilots always maintain as much altitude as possible until they are ready to land. If the plane looses power you want as much time and distance as possible to glide the plane to a clear landing spot.

@NoahSpurrier that has nothing to do with what is being asked

Airplanes prefer to land in a headwind. This reduces their groundspeed compared to landing with the same tailwind.
Braking distance grows quadratically compared to groundspeed. So any significant reduction in groundspeed is worth having.
Successive airplanes should all come from the same direction to land. This removes any danger of collision when a plane fails a landing and goes around into what would otherwise be oncoming air traffic. Planes also prefer to take off into  headwind, so if takeoffs are intermingled with landings (very common in a busy airport) they won't interfere with each other if they all go the same way.
The tower monitors the wind and then decides which way the airplanes should come in to land and directs landing craft to land from that direction.

-1 for being too generic: while the information here is correct, I don't think it answers the specific question stated by the OP.

@kevin Au contraire. I especially liked that this answer was tailored towards the obvious non-existance of any prior knowledge in the OP. Compare with Geocrafter's answer, which, while technically correct and ultra specific, is almost worthless to the OP, because it's loaded with aviation lingo and places the wind and serialization aspect as an aside. OP appeared to need a general answer worded for a non-aviation receipient.

@kevin I think you're interpreting the question as being more specific than it is.

@kevin What exactly do you think the specific question is that this doesn't answer? The exact wind speed and direction? What the ATC was thinking?

@Kevin it does not address the U-turn. The answer is not planes land headwind: tailwind landing can be done as well. The answer is the STAR terminates in the opposite direction of runway heading. Most STARs terminate by aligning the plane with the runway, hence the approach experienced by the OP is unusual (while not rare), hence the question.

@kevin that is not true and that's why IAF and FAF are not the same thing. This answer is very good and you are just nitpicking. Obviously, when the aircraft arrives from a different direction than  the runway in use direction, it will have to turn somewhere. I really find that obvious enough no matter where some STAR terminates.

could there be more kevins

I'm surprised at how few people agreed with @kevin that this doesn't address the question. This answer focuses on "why approach the runway in a particular direction?", but the OP makes clear they are not asking this: "I thought it might have been a need to adjust for the runway" and "if it was just a matter of adjusting the direction for the runway...". No, the OP is asking why the u-turn was done in the way it was: "we went quite a way past the airport", "what would be the need to keep the high altitude and go so far to make the U-turn", and "some flights coming from the west do that move"

It's even in the title: "Why might an airliner fly a large U-turn before landing?" (emphasis mine), and the meaning is still clear on the original unedited post's title: "Reason for a big U turn before landing".

@JBentley In that case the title is far from clear, quite the opposite to me. What is a large U turn? For me that is not a long downwind leg, but a turn with a large diameter or with a large centrifugal force or something like that.

@hiergiltdiestfu - One of the best comments I have read on this site.  Others should take heed.  Often it seems respondents are more interested in showing off their knowledge in the battle for reputation points than in assessing the knowledge level of the questioner and tailoring their response accordingly.

As a Virtual Controller on vatsim.net at Toronto, I can tell you the following:

Depends on runways, most of the time they operate runways 24R and 23, which lands planes facing south west. Runways are chosen from the wind direction, as planes preferably land into the wind. Winds at Toronto just most likely will favor the 24 runways.
The STAR(s) "Standard Terminal Arrival Routes" coming from the west puts planes in a direction that is completely opposite  (downwind) direction for runway 24R or 23, then get directions (vectors) to align with the runway by a controller.
The approach airlines mostly fly into Toronto is the ILS which you can think of like a beam coming from the runway that lines the plane up with the runway hence for the plane the intercept that beam, the plane cant be turned in right away. Therefore, ATC will turn the plane perpendicular to the runway, then a 30 degrees difference to the runway for the aircraft to intercept the beam.

Here is an image of how it looks like:
Example approach. Big light blue arrow indicates what the wind direction may have been like. See: What determines in which direction a runway is used?
Here, the plane is coming from the South-West, following GPS locations until the downwind. It then gets turned inbound for the ILS.

ILS = instrument landing system.  "A radionavigation system which provides aircraft with horizontal and vertical guidance just before and during landing and, at certain fixed points, indicates the distance to the reference point of landing." — Article 1.104, ITU Radio Regulations (ITU RR), p. 16, https://www.itu.int/dms_pub/itu-s/oth/02/02/S02020000244501PDFE.PDF

What is a virtual controller? You get paid or just do that for hobby?

@Cloud, it means he plays video games.  In my mind that dilutes credibility, although his answer is fair enough to stand on its own merit.

I think the other answers have covered the "Why U-turn" part well, but to address the other part about why so far past

I thought it might have been a need to adjust for the runway, but as I said, we went quite a way past the airport, meaning after the turn we had to fly "a little bit to get back to the airport". All that even before starting the process of descending for landing (if it was just a matter of adjusting the direction for the runway, what would be the need to keep the high altitude and go so far to make the U-turn?).

I most often travel through Harsfield-Jackson in Atlanta (busiest in the world) and doing the long U-turn is pretty common. The reason it's so long is that you're getting in line behind all the other traffic. I've watched the plane I was on pass as many as a dozen other aircraft before turning and falling in line (this is less common now since they've added more runways).
By contrast, flying into a smaller airport with less traffic often involves very little distance between passing the airport and turning. On one occasion we were running late into Jacksonville, FL due to an equipment malfunction in ATL. The pilot pulled a fairly sharp turn on that one when we were just past the airport. We had barely straightened up before we were over the runway.

Yeah, you typically fly a pretty long downwind at ATL. It's kind of neat to drive through or fly over Atlanta when it's dark, as you can see two giant swirls for the traffic patterns headed into the North and South arrival runways. Flights from Florida to Nashville frequently fly over midfield at ATL, so they provide a neat view of the traffic patterns if it's dark out.

Weather could be a factor. For full ils you might want to be lined up with localizer for a few miles before the glide slope is intercepted. Also wake turbulence for larger aircraft. Also noise abantmance. Some times they let them do short finals too.

I live about 100km west of Pierson Airport at Toronto and can inform you, as others have mentioned, the runways used and landing /takeoff direction is dictated by the current prevailing winds.
My house is situated directly under the flight lane from a local beacon to Toronto, and I can tell which way the wind is blowing simply by listening and watching the aircraft go overhead.
When there is an east wind and at the peak time of day, around 5pm - 7pm, aircraft will fly overhead at a regular separation distance on their decent approach to the airport. When winds are from the west they pass MUCH higher overhead.
Air traffic control vectors the aircraft into this line. When the wind blows from the east, aircraft that arrived in Toronto from the east fly past the airport and, if I look east from my house, I can see them turning into gaps in the line at appropriate separation distances. If no gap is available due to traffic, they circle at appropriate, stacked, heights till a suitable gap opens up. The lowest aircraft joins the line and any remaining aircraft drop down a level in the stack.
The prevailing winds in this part are normally from the west, so most of the time all this happens to the east side of Toronto, as it was in your case.
Intrestingly, since the incident with Air France Flight 358, when a storm is happening, aircraft are now stacked from both directions during severe weather events at the airport.
The busier the airport the more complex all that stacking becomes. The image below is for London, Heathrow. Note they have stacks for planes approaching from the four corners of the compass that are then filtered into two runways as appropriate by ATCs. Again, this whole setup will reverse depending on wind direction.
(Image source)

The prevailing wind at Heathrow (and, indeed, in most of the UK) is from the west, so the diagram shows the most common scenario.

FYI, the reason that the arrows between the stacks and the runways are so fat is that exactly where each plane turns will vary as needed to establish proper separation for merging traffic streams and variations in the ground speed in each direction due to wind intensity.

It looks suspiciously like the NUBER2 STAR into CYYZ, possibly with radar vectors early for traffic or weather separation/deviation, followed by radar vectors to the initial fix for either a visual or instrument approach to RWY 24 L/R.

Shared rules must meet everyone's requirements
First, aircraft land in a headwind, hence the U-turn.
They're in a stack of other aircraft approaching, so they have to "get in the queue". Even if this Cessna could easily tailwind-land on a 10,000 foot runway in the tailwind, the 777 behind it really shouldn't.
Making the stream of aircraft manageable requires a standard approach.  As you can imagine, this is "lowest common denominator" to accommodate all aircraft.
A lot of work to do: stabilizing the approach
Why is it so long?  Because there's a lot of work to do.  The pilots' time is a chokepoint, that is to say it's a high workload time.   If the work isn't done, they can't land and have to go around.
They have to either find the localizer (horizontal beacon) or get roughly lined up on the runway.  Then they have to line up vertically on the glideslope beacon (or the four lights which are a visual version of the same thing).
They have to get their speed where it belongs (several times during the approach), get power where it belongs, drop landing gear, set flaps in coordination with their speed reductions, work their checklists, and prepare the aircraft in all other respects.
If they are dealing with crosswinds, they also must have a strategy to correct for that.
All this is called "stabilizing the approach".
Then they reach a decision point called "minimums", some ways back depending on their flight mode.  Here they decide whether they are able to continue the landing: Can they see the field? Is the approach stablized? Continuing to press a bad approach is a bad habit.
So the approach pattern is long to give everybody time to do this.
Also, that approach is slow
The final (upwind) leg of the approach also has the slowest airspeed of the whole flight, and it's into the wind.  So it will tend to take a lot longer than the downwind leg where you flew past the airport.  So it may seem like it's really far, when it's just really slow.

Although it felt strange to you, it is very common. For efficiency reasons, sometimes it occurs at large airports that aircraft land on a direct approach. But, in general aviation, what you saw is completely standard..

Do you perhaps have this backwards? The asker was on a commercial flight to a large airport. At large airports, it's much more efficient for everybody to land (and take off) in the same direction since you can pack vehicles moving in the same direction much more tightly than vehicles moving in opposite directions.

Precisely. In order to have everyone land in the same direction, a pattern is established.

You describe everybody landing in the same direction as completely standard in GA. However, you begin the sentence with "but", which suggests that this situation is different the previous thing were talking about (large airports). It's not different at all. Indeed, at large commercial airports, it is more important for everybody to land in the same direction, because it's the only way you can possibly get the throughput. At an airport with only a few plane movements an hour, it wouldn't affect throughput at all.

@DavidRicherby The difference he was referring to is more applicable for the case of traffic arriving from the direction where they would already be on-course to the current runway direction. At controlled fields, this traffic will often just be vectored straight onto final. At uncontrolled fields, it's more customary (at least for VFR traffic in the U.S.) to still fly past the airport and enter the pattern 45 degrees to the downwind (opposite direction of runway traffic) and then turn base to final (which is the "U-turn" that the OP asked about.)

Pilots always maintain as much altitude as possible until they are ready to land. If the plane looses power you want as much time and distance as possible to glide the plane to a clear landing spot...
runways are always entered from one direction for all traffic. If you approach a runway from the wrong direction then you have to make a u-turn and come back to turn downwind to face the runway. the course your plane took may have been extended for spacing other planes or the pattern may have appeared long to your sense of scale. Large planes fly fast and need a lot of space to turn around while maintaining safe distances from other aircraft.
Small airports fly a standard clockwise pattern that always uses a u-turn. Larger airports with air traffic control and instrument guided approaches will have approach patterns published in charts. Unless otherwise instructed pilots entering the airport airspace are expected to use the published approach; although really an approach would never be made without contacting air traffic control.

This answer mostly explains "what" rather than "why". Essentially, you're saying "There's some procedure that requires pilots to do this", which is good to know but doesn't really explain why the asker's plane took the route that it did. Why are these procedures in place?

authors: Vladimir F Героям слава


text:
What infrastructures are required for airlines to send PNL messages?
There are lots of information about Type-B messages sent by airlines on IATA website but they have not stated under what communication systems (cable, teletype, intranet, internet, etc.) these messages are exchanged. What are these systems?


text:
Why does Airbus A380 have only reversers on inner engines?
I have seen many videos, and I noticed that only the inner engine reverses were opened. Why not on the 4 engines?

Related: http://aviation.stackexchange.com/questions/6361/why-doesnt-the-a380-use-its-outboard-thrust-reversers?rq=1


text:
Is there any ATS into the Special Use Airpaces (SUA)?
The SUA has its own characteristics and limitations. Is there any unit responsible for providing separation, control or information, for pilots flying into or across any SUA?

Are you asking about a specific country (the US?), or in the general?

Related: Restricted Area “popping up” around you — can it happen, and what do you do about it? ⌁ and ⌁ What are some examples of warning areas and restricted areas?

In many cases, there are controllers dedicated to providing ATC services to the aircraft that are USING the SUA.  Callsigns such as "Nellis Range" or "Eglin Mission" are used for the controllers working with aircraft within the SUA, be it MOA or Restricted or Warning areas or whatever.  What looks like one big chunk of airspace on the chart may likely be divided into separate areas for training or testing purposes that the aircraft flying into it will know about, and it's useful (sometimes, vital) to have a controller monitoring the various missions and keeping the various aircraft apart.
These controllers may work in a dedicated facility that only deals with military aircraft, or they may work within a larger facility that includes "regular" ATC functions as well.  For instance, the controllers who work the off-shore warning areas south of Eglin AFB as well as the on-shore restricted areas east and west of Eglin are physically located in the same RAPCON that is Eglin approach.  So civilian aircraft inbound to Crestview or Destin or Eglin/Ft Walton Beach are talking to controllers working one set of scopes, but across the room are the controllers for Eglin Mission who are watching the various SUA.  An aircraft that departs Eglin (or Hurlburt, or Duke Field) would probably be talking to one of the former initially, then when they head into one of the restricted or warning areas, they'd be handed off from "Eglin Approach" to "Eglin Mission."  Essentially it's like being handed off from one Approach sector to another, just that the Mission controllers have slightly different roles in keeping the airspace safe.
It's far better to clear an aircraft transiting a particular sector of SUA to fly through it ABOVE the aircraft in it that is employing air-to-ground ordinance, for instance, than clearing him through the airspace BELOW the bomb-dropper!  Or, if necessary -- maybe it's a helo with an emergency that needs a straight line return to base and isn't going to climb up very high -- at least you have the bomb-dropper go cold and hold up high until the transiting aircraft is out of the way!  That's the sort of ATC that Eglin Mission does that Eglin Approach doesn't... along with confirming that this callsign is in fact scheduled for this range at this time, and the last aircraft has departed, so "you're cleared in to Range XYZ to work surface to 15,000', advise 5 minutes prior to departing."
Fun times!


text:
What is the name of this wing area?
What's the name of this wide area connecting the wing to the fuselage?

Does this wide area closest to the fuselage on some wing designs has a name?

Yes it does, but please note that you have two different kind of widenings in your pictures. In the first picture the widening goes backward, while in the second picture it goes forward.
The backward widening in the first picture is termed "Yehudi" and it is normally implemented on jetliners in order to accommodate the main landing gears and for other aerodynamic and structural reasons, as nicely explained in this answer:

The forward widening in the second picture is termed "leading-edge (root) extension" (aka "strake") or "chine". It basically works at "high angles of attack, generating a vortex flow over the inboard wing to stabilise the airflow and increase its speed locally, thus delaying the stall and also providing additional lift". This vortex generated by the strake is nicely visible in the following picture from this NASA report, where you see half of a wing being tested in a wind tunnel:

Strakes are mostly seen on jetfighters exactly for that reason but on the Rutan VariEze in your second picture they have been most probably implemented in order to:

increase the wing area and especially to increase it forward to shift the aerodynamic center forward as well, something which is always good in a canard design;
"increase directional stability, by reducing the adverse effects of crosswinds or yaw on the forward fuselage. Unlike a conventional fuselage, the chines allow the crossflow to travel smoothly over their profile and beyond, avoiding the side forces due to flow separation and stagnation";
improve stall characteristics; the downwash released by the canard interacts with the vorteces generated by the strakes (seen in the previous picture), further increasing wing lift at high AoA, something which is of paramount importance on a canard design where the canard is supposed to "stall" before the wing.

A VariEze being tested by NASA. The strakes are clearly visible from this perspective.

In the top example it's more of just a change in taper.

According to Boeing lore via George Schairer, yehudi's are named after Yehudi Menuhin, because no one could understand how the trailing edge extension improved the B-47 aerodynamics, just as no one could understand how Menuhin played the violin so well.

@sophit small increases in leading edge sweep on airliners are often referred to as "gloves".

It is called the wing root.
From Wikipedia:

The wing root is the part of the wing on a fixed-wing aircraft or winged-spaceship that is closest to the fuselage

It can also be used to describe the area right where the wing connects to the fuselage.


text:
Does zero-lift angle of attack depend on Reynolds number?
In this post I read that, due to viscous effects, the $C_{l}$ at a given angle of attack increases slightly with the Reynolds number but it seems that it just happens near the stall angle of attack.
I am performing some wind tunnel experiments at much lower Reynolds than those of the figure of the linked post (150,000 and 300,000) with the same profile, NACA 4412. My question is if at the mentioned Reynolds, can there be a small variation in the angle at which $C_{l}=0$, and therefore my $C_{l}-\alpha$ curves at Re=150,000 be noticeably below the Re=300,000 ones.

What results are you seeing from your experiments?

I am having some repetitiveness problems at the lowest Reynolds and I planned to use this as a criteria to rule out data. However It seems that it depends and, although very slightly, it decreases as Re increases.

The aerodynamic coefficients  $c_l,c_d,c_m$ are in general functions of the angle of attack $\alpha$, Reynolds $Re$ and Mach number $Ma$. For your experiments, since you are operating in a very low $Re$ regime, assuming incompressible flow, your lift, drag, moment curves will largely depend on viscous phenomena (i.e. $Re$ number). Generally, as $Re$ number drops, the boundary layer thickens. For this reason, you will expect a lower $c_l$ number (due to viscous decambering) and a higher $c_d$.
You may also discover non-linear behaviors even on operating angles due to laminar separation bubble forming/bursting on the suction surface and this is very dependent on the turbulent intensity of your wind tunnel so the stall angles and post-stall behavior may not be the same for flight conditions where turbulent intensity is very low.
Finally, you can confirm with Xfoil that for $Re=300k \Rightarrow \alpha_{L=0}=-4.33\ deg$ while for $Re=150k \Rightarrow \alpha_{L=0}=-3.64\ deg$ for the NACA4412.


text:
Are there any simulators around to simulate ADS-B data (TIS-B & FIS-B)?
I am trying to find a simulator like the Spirent GPS Simulators. Are there any Simulators out there which can simulate and generate random traffic and weather information for TIS-B & FIS-B testing?
I have an ADS-B 978 UAT receiver hooked up to an antenna which receives signals mostly from 1 tower. I would like to hook up a simulator to the UAT receiver which can simulate the ADS-B data block (customized). I tried searching via Git and many other places couldn't find one.
Has anybody came across any such a thing? Objective - TIS-B to generate random traffic, FIS-B to generate necessary weather.

How do you search with git?

@Steve https://github.com/git and use the search box in the upper right of the page. I tried "ads-b" and "ads b" and found no repositories with those terms in the their title.

most of the software I have seen is to decode ADS-B data. Here's the searches I get at github for "ads-b" https://github.com/search?p=2&q=ads-b&type=Repositories&utf8=%E2%9C%93

While this can probably be done with a SDR, I would be very weary of doing it outside of a lab environment. The problem is that you can't contain the signal and while it probably won't travel far, a low flying aircraft directly overhead may pick up your simulated signals. You may want to look into something you can hook directly into the antenna port so you aren't actually broadcasting bad data, but I'm guessing if you have that kind of budget you wouldn't be looking for open source software...

@selectstriker2 Ah, GitHub. That's a service. git is the version control system.

@RonBeyer I will not be broadcasting the data. So far whatever I searched returned all decoders of real time data. My Intention is to generate the ADS-B data just like a ground station. (mimic it) in closed and wired method. In that way I would be able to generate a random traffic or weather with my own customization.

I am developing a display software system which I would like to test it is capable of all combination of weather and traffic. Right now, I am at the mercy of the real broadcast.

Aeroflex IFR-6000
From the manufacturer's website:

The Aeroflex IFR 6000 is a compact, lightweight and weatherproof unit designed for testing transponder modes A/C/S, TCAS I and II as well as DME. Includes antenna shield and hard transit case. The IFR 6000 features an extremely easy to use interface where every parameter the user commonly needs to view is displayed on screen.
Dedicated Mode keys for XPDR, DME and TCAS allow quick selection of the operational mode. The application dependent softkeys and data select/slew keys provide an intuitive man machine interface. DME mode is provided with dedicated keys for frequency/channel selection and RF level control.
For frequently varied parameters in DME and TCAS modes, such as Range and Rate, dedicated keys are provided. Each operational mode has one main user screen. The operational modes are: XPDR (Sub-Modes: ADS-B MON, ADS-B GEN & GICB) DME TCAS 1, 2 (Sub-Modes: TIS) Most tests can be completed without leaving the main user screens. This simplifies the line technician's testing task.

However, it is subject to stringent export restrictions. If you are outside of the US, it is not available to you.


text:
How does blade solidity ratio relate to thrust/power/torque of a propeller?
for quite some time I was using ABBOTT formula for static thrust estimation on a two-bladed propellers:
$$
T=6.8\times10^{-5}\times D^{3}\times p\times RPM^{2}
$$
$T$ is Static Thrust (N); $D$ is propeller diameter (m), $p$ is propeller pitch (m); RPM (1/s)
I was, however, unable to find any formula which would include number of propeller blades.
Standard thrust estimation methods all seem to rely upon the "propeller disk area" which is always assumed for a two-bladed propellers.
The closest I was able to get is something called "blade solidity ratio", or "rotor solidity":
$$
\sigma = (B c)/2\pi R
$$
where $B$ is number of propeller blades, $c$ is chord of each blade, $R$ is radius of the rotor.
The question is - how does blade solidity relate to thrust/power/torque?

You'll find this info in helicopter performance design literature. The power to drive the rotor (and a propellor) can be sub-divided into three parts: useful power, induced power, and profile power. The solidity ratio shows up in the profile power part.
Like in fixed wing aerodynamics, the power/thrust equations are often made dimensionless and evaluated in coefficients. From Helicopter Test and Evaluation by Cooke and Fitzpatrick, section 2.4:
$$C_P = C_T \left( \frac{V_C + v_i}{V_T} \right) + \frac{s \cdot C_D}{8} $$
with $s$ = solidity ratio, $V_C$ = climb speed, $v_i$ = induced velocity, $V_T$ = blade tip speed. So solidity ratio shows up in the profile drag power portion, which makes sense.

Each propeller blade is a wing in itself, and like a wing carries the weight of the plane, the propeller blade carries its fraction of the total thrust of the propeller. The more blades, the lower the fraction of each blade.
Low disc loadings are associated with two- or three-bladed propellers. Those can be found on GA aircraft and older, slow designs like pre-WW II aircraft. With turboprops and near-transsonic designs, more blades are needed to distribute the aerodynamic loads and to reduce the lift coefficient especially at the tips.
There is no strict formula, but in general a higher disk loading is associated with a higher solidity ratio.

Let's calculate the thrust given by a blade of airfoil NACA 0012, length r, constant chord c, and pitch p (constant along the blade). Prop turns at Omega rad/s. Derivation taken from https://aviation.stackexchange.com/a/80626/16042
All units SI. The pitch angular value p is in radians.
The differential expression for the thrust given by element area ds=dr·c of one blade is: $$dL=2,86\cdot c\cdot \rho \cdot (p\cdot \Omega ^{2}\cdot r^{2}-w\cdot \Omega r+p\cdot w^{2}-w^{3}/\Omega r)\cdot dr$$
This expression accounts indirectly for the solidity of the propeller, since the chord is one of the variables. And, after all, as solidity s= c/π·r, the differential expression above may be re-written inserting s·π·r in place of c…
Going back to the original differential expression above, and for constant values of chord, air density, inflow, prop angular velocity and blade pitch, we may integrate only the first term, since in the static case inflow is zero or close to zero. So we have that, for one blade:
$$L=2,86\cdot c\cdot \rho \cdot p\cdot \Omega ^{2} \int_{0}^{r}r^{2} dr$$
Inserting values for an example two-blade propeller with blade length 0,86m, Omega = 2124 rpm = 222 rad/s, rho = 1,23 kg/m3, chord = 0,12 m, blade pitch = 14º = 0,244 rad
$$L=2,86\cdot 0,12\cdot 1,23 \cdot 0,244\cdot \ 222^{2} \int_{0}^{0,86}r^{2} dr$$
Integrating…
$$L=2,86\cdot 0,12\cdot 1,23 \cdot 0,244\cdot 222^{2}\cdot  0,86^{3}/3$$
We end up with a thrust of 1076 newton per blade… That’s 2152 N for the two-blade prop. Almost the same value as with Abbott’s formula… (Values for pitch & chord duly tweaked so that the result agrees with Abbott's…)